The present invention relates to a xerographic apparatus for forming images on paper, such as a copying machine; fax machine; laser printer; LCD or LED printer; or a multi-function device enabling a combination of these functions.
The concept of xerography was pioneered by Chester Carlsson in the pre- and post-war years and is well documented in patent and other literature. This work resulted in the first commercial photocopiers in the late 1950""s and further developments in the 1960""s and 1970""s. Throughout this time efforts were made to make the machines cheaper and more compact; and less reliant on service visits from qualified technicians.
A watershed event in ease of service was a development by Canon KK detailed in U.S. Pat. No. 4,538,896 which discloses a process unit which is removable from the main image forming unit and is intended to be discarded. This allows the user to perform a preventive maintenance task without specialised assistance from a service technician.
Since then, Customer Replaceable Units (CRU""s) have become commonplace especially in smaller machines dedicated to office and home environments. The CRU may contain one or several assemblies and components which require replacement on a preventative maintenance basis. Typically this may include at least a toner tank for the supply of fresh toner or developer and a waste tank for accomodation of depleted toner or developer. These two vessels usually constitute a significant volume of the CRU.
An example of a CRU predominantly containing these two tanks can be found in U.S. Pat. No. 5,126,799 reissued as RE 35528. In this invention Ricoh Company define a xe2x80x9cCleaner Toner Magazinexe2x80x9d (CTM) comprising a toner supply tank and toner recovery tank, joined together as a detachable magazine for user replacement.
As the popularity and number of CRU models has increased, a significant industry has evolved dedicated to the refilling and refurbishing of CRU""s. So whilst the Original Equipment Manufacturer may seek to group elements requiring similar replacement intervals into single CRU""s, the Refiller may seek to further subdivide the preventative maintenance elements and replace those elements within the CRU that wear the fastest and salvage those elements which may be reused for a further cycle.
It is an object of the present invention to provide a service unit for an image forming apparatus which maximises utilisation of parts which have long life.
In a preferred embodiment the present invention utilises one or more flexible diaphragms to optimise the volume use within a CRU, by allowing fresh toner to occupy a greater proportion of the internal volume at the beginning of life and a lesser proportion of the available volume as the fresh toner is depleted. Conversely the volume available to the depleted or waste toner can be increased during CRU life at the expense of volume dedicated to fresh toner.
Thus the compactness of the CRU can be improved or alternatively the life of the CRU may be extended within the same design and space envelope.
A further embodiment of the invention allows recharging of the CRU itself by supplying the flexible toner reservoir in the form of a disposable or reusable cannister. New cannisters, filled with an appropriate supply of toner can replace spent ones in the CRU.
This allows Remanufacturers to recycle spent CRU""s and maximise the utilisation of those parts which are not subject to wear or depletion. As the toner is supplied in a cheap cannister, the need for toner bottles is eliminated.
The invention will now be described by way of example and with reference to the accompanying drawings in which: